Black & white continuous tone printing using multiple negative working plates, so that each plate prints an equal segment of a determined density range

Rochester Institute of Technology

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Theses

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5-1-1986

Black & white continuous tone printing using

multiple negative working plates, so that each plate

prints an equal segment of a determined density

range

Frank C. Forti

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School of Printing

Rochester Institute of Technology Rochester, New York

CERTIFICATE OF APPROVAL

MASTER'S THESIS

This is to certify that the Master's Thesis of

Frank C. Forti

with a major in Printing Technology has been approved by the Thesis Committee as satisfactory for the thesis requirement for

the Master of Science degree at the convocation of

May, 1986

This is to certify that the Master's Thesis of

Frank C. Forti

with a major in Printing Technology has been approved by the Thesis Committee as satisfactory for the thesis requirement for

the Master of Science degree at the convocation of

May, 1986

Thesis Committee: ---Thesis Advisor

Graduate Coordinator

BLACK & WHITE CONTINUOUS TONE PRINTING USING MULTIPLE NEGATIVE WORKING _PLATES,

SO THAT EACH PLATE PRINTS AN EQUAL SEGMENT OF A DETERMINED DENSITY RANGE

by

Frank C. Forti

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the

School of _Printing in the College of Graphic Arts and _Photography of the Rochester Institute of _Technology

May, 1986

THESIS RELEASE PERMISSION FORM

ROCHESTER INSTITUTE OF TECHNOLOGY

COLLEGE OF GRAPHIC ARTS AND PHOTOGRAPHY

Title

of

Thesis:

BLACK

&

WHITE CONTINUOUS TONE PRINTING USING

MULTIPLE NEGATIVE WORKING PLATES, SO THAT EACH--rLATE

PRINTS

AN

EQUAL SEGMENT OF A DETERMINED

I,

Frank

C.

Forti,

herby

grant

permission

to

the

Wallace

Memorial Library of R.I.T., to reproduce my thesis in whole or in

part. Any reproduction will not be for commercial use or profit.

---- -. - - - -...- . -... .. ...~

...

...

-.

ACKNOWLEDGEMENTS

I would like to thank _my advisor, Dr. J. L. Silver, for his

ideas and suggestions. I would also like to thank Mr. Sven

Ahrenkilde, who was always there to _help me, and to Professor

Frank _Cost, Professor Joseph _Noga, and the rest of the School of

Printing faculty for their support. Special thanks to the T&E

Center for the use of their _equipment, and their willingness to

help. And _finally, I thank _my parents and _my whole _family for

their constant support and encouragement.

TABLE OF CONTENTS

PAGE

LIST OF TABLES v

LIST OF FIGURES vi

ABSTRACT vii

CHAPTER ONE INTRODUCTION

Screenless vs. Halftone _Printing 1

Collotype Process 2

Random Dot _Printing 2

Subtractive Positive _Working Screenless System 3

Negative _Working Plates 5

Statement of The Problem 7

Hypothesis 7

Footnotes for Chapter One 9

CHAPTER TWO RELATED LITERATURE

Screenless _Lithography in Relation to Plate Grain 10 Tone Reproduction in Screenless _Lithography 11

Footnotes for Chapter Two 14

CHAPTER THREE -- METHODOLOGY

Film and Plate Preparation 15

Evaluation of Results 21

Footnotes for Chapter Three 22

CHAPTER FOUR PRESS TEST AND EXPERIMENTAL RESULT

Evaluation of Press Run 24

Second Press Run and Test Evaluation 32

CHAPTER FIVE CONCLUSIONS AND RECOMENDATIONS

Summary and Conclusions 41

BIBLIOGRAPHY 43

LIST OF TABLES

TABLE 1 Exposure and Developement Times to Produce the

Negatives 19

Photographic Masks 19

Density Readings of Negatives 20

Plate Exposures/First Press Run 21

Density Readings From Printed _Step Wedge 28

Exposure and Developement Times for Negatives

for Press Run Two 30

Photographic Masks 30

Density Readings From Negatives 31 Plate Exposure Times/Second Press Run 32

Density Readings From Second Press Run 34 Densities of DuPont Scales used in Plate Test... 39

TABLE 1A

TABLE 2 TABLE 3

TABLE 4

TABLE 5

TABLE 5A TABLE 6

TABLE 7

TABLE 8

FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 9 FIGURE 10 FIGURE 11 FIGURE 12 FIGURE 13 FIGURE 14 FIGURE 15 FIGURE 16 FIGURE 17 FIGURE 18 FIGURE 19 FIGURE 20 FIGURE 21 FIGURE 22

LIST OF FIGURES

Grained Positive Plate 4

Positive Plate Exposed 5

Processed Positive Plate 5

Grained Negative Plate 6

Negative Plate Exposed 6

Processed Negative Plate 6

Effective Tone Reproduction in Screenless

Lithography 12

Mask Representation for Plate One 18 Mask Representation for Plate Two 18 Mask Representation for Plate Three 18

Plate _One/ First Press Run 25

Plate Two/ First Press Run 26

Plate _Three/ First Press Run 27

Tone Reproduction Curve/lst Press Run 29

Tone Reproduction Curve/2nd Press Run 35

Plate One/ Second Press Run 36

Plate Two/ Second Press Run 37

Plate Three/ Second Press Run 38

Plate One. Plate Exposure Test 40

Plate Two. Plate Exposure Test 40

Plate Three. Plate Exposure Test 40

Plate Four. Plate Exposure Test 40

ABSTRACT

Continuous tone _printing, either collotype or screenless lithography, are processes that are in limited use. The halftone

method of _{reproduction is still the most economical}

way to

reproduce a continuous tone original. This _study dealt with the

mechanism of screenless _lithography, more _specifically on how to

make the use of negative _working plates a feasible alternative to positive _working plates.

It is known that the positive _working plate can print a longer range of tones than a negative _working plate. So the main

point of the experiment dealt with how to extend the range of a

negative _working plate. A negative plate is of high contrast, and

so multiple negative _working plates were used to print one image. Each plate in itself can print three to four steps of a

continuous tone _step wedge. In this _experiment, three plates were

used in the hopes of _printing twelve steps in a continuous

gradation. A continuous tone _step wedge _along with a black and

white photograph were divided _among the three plates. Twelve steps on the _step wedge were _identified, and so each film had four of the possible _thirty steps which existed on the _step

wedge. These films were exposed to _plates, and mounted on the

press. Each image was run in registration with one _another, and

the solid ink _density was varied to produce the continuous tone

effect. From the press sheets examined, in which there are

examples in this _report, a high contrast image was produced.

One of the main problems in the experiment was differences

in emulsion _coating on each individual plate. Which resulted in

inconsistent exposure times from one plate to another. From

repeated plate _{testing using} a .15 density increment continuous

tone _step wedge as a control _guide, it was found that for the

same exposure a _hardening of the plate _coating (and consequently of ink _{receptivity) corresponding} to two steps _equaling .30

density difference was to be expected. This made it _virtually

impossible to get a handle on the correct exposure time needed

for the plate.

Results from this experiment show, that it is not possible

to effectively print a continuous tone image with a negative

working plate and or multiple negative plates. This is due to

the high contrast of the negative _{working plate,} thus _making

it suitable for _mainly halftone lithographic purposes.

CHAPTER ONE

INTRODUCTION

Screenless vs. Halftone Printing

Today almost all pictures that are reproduced economically

are reproduced _using the halftone method. This conversion of a

continuous tone original into a pattern of dots degrades the

image and introduces problems in the reproduction process. The

resolution of the image is limited _by the size of the _dot, thus

were fine detail is needed the use of the halftone process will

not achieve the desired results. A effect is also a

problem with the halftone process, caused _{by overprinting}

halftone images, or _by screen interference with irregular shaped images in the subject. Another example of degradation is

experienced in color reproduction when pastel colors in originals

(which are always continuous _{tone) usually} turn out grayer or

less saturated in the halftone reproduction. That this saturation

loss is due to the halftone structure can be demonstrated _by

exposing both continuous and halftone scales onto a photographic

color film. The continuous tone highlight steps will have higher

saturation than the halftone even though _they are matched for lightness and produced _by the same dyes. These problems can be

of the screenless process is limited because of problems

controlling the process.

There are two systems of continuous tone printing, the

collotype _process, and random dot printing. These two processes

will be explained in the _following two sections. Through out this

paper, the terms "random dot printing"

and "screenless

lithography"

will be used in reference to the same process.

COLLOTYPE PROCESS

The collotype plate consists of a _{differentially}

light-hardened "image" that picks _up ink in direct proportion to the

degree of _hardening of the gelatin. The plate is coated with a

dichromate gelatin, which is applied while the plate is _spinning

on a plate whirler. This process has not been that _popular,

because it is _{very involved,} and also the number of impressions

off one plate is limited to about two thousand.

RANDOM DOT PRINTING

Random dot _printing is called a continuous tone _process,

though the printed image is not a continuous film of _ink, but is

made _up of _randomly distributed spots of ink that _vary in size

3

and are _irreguarly shaped. The tones produced are of a

resolution greater than that of a 300-lines/inch halftone screen.

grain structure of the plate to produce a suitable gradation of

tones. Pearson and _Pobboravsky determined in their _study that

the grain of the plate was the _key element in _producing a

continuous tone _effect, because a smooth surface did not show the

effect while those with a _grainy surface did. _They also ruled out

the possibilities of the grain of the continuous tone image used

to expose the _plate, and also the the grain of the ink stucture.

The type of plate used in random dot printing is a subtractive

positive _working plate. The additive systems typified _by the

chromate sensitised colloid deep-etch methods yield _extremely

contrasty screenless responses. In this respect, they are not

unlike those _appertaining to 'lith' silver halide photographic

emulsions, being completely unsuitable for this application.

Subtractive Positive Working Screenless Plates

A positive _working plate is coated with a diazo oxide

emulsion, which on exposure to light becomes soluble this means

where there is more exposure there will be more _coating removed.

The grain of the plate is a series of peaks and _valleys, and in

the case of a positive plate the _coating sits in these valleys.

This is shown in Figure 1. Also, since the _coating is first

destroyed at the peaks where it is _thinnest, it would be _likely

to predict that a positive _working plate would print lighter

tones from the valleys of the plate grain. The films used to

range of about 1.0. For _instance, for the ST Positive

Con-Tin-Tone wipe-on _plate, a highlight _density of 0.40 and a

Q

shadow of 1.40 was found to work best. This information was

current as of 1966.

The exposure of continuous-tone positives to the plate is

critical. Overexposure produces excessive sharpening, while

underexposure has the opposite effect. Registration on press

must be almost _perfect, a slight misregister can not be

tolerated. Though this is not the case with halftone printing,

where a slight misregister will not _necessarily affect the image.

Inks and paper are less critical. Inks which run well for

halftone _printing are _satisfactory for continuous tone

. .. 10

printing.

With the use of a subtractive positive _working plate in

random dot printing, it is possible to get as _many as 50,000

impressions out of a plate.

MECHANISM FOR POSITIVE WORKING GRAINED PLATES

Figure 1. This is a positive _{working coating} on a grained

Figure 2. This plate has been given an increasing amount of

exposure _starting from left to right. The exposure was greatest on the right hand _side, so it shows the greatest depth of

solubilized coating.

GRAINED ALUMINUM PLATE

Figure 3. This is the plate after processing,

NEGATIVE WORKING PLATES

Negative _working plates work on the mechanism of

photo-insolubilization. Exposure through the continuous tone

film, results in different depths of insoluble material within

the _{coating layer,} and _only material transformed in immediate

contact with the plate surface is retained on processing. The

coating hardens from the top down, so in areas where there is less exposure the _coating will not be _totally adhered to the

plate. Thus, when this plate is processed the _coating which is

not _totally insolubilized will be washed away. The _coating sits

on _top of the grain of the plate, and sometimes on press certain

areas which did not recieve enough exposure will be rubbed off

the plate. This is because there is a lot of abrasion between the

plate and the blanket. The following diagrams show the mechanism

MECHANISM FOR NEGATIVE WORKING GRAINED PLATES

LIGHT SENSITIVE COATING

Figure 4. Light sensitive coating on grained aluminum plate

Figure 5. The plate has had an _increasing amount of exposure

from left to right. Insolubilized coating is shown _by cross

hatching. The right side of the plate recieved the greatest

amount of exposure, thus it has the greatest depth of

insolubilized coating. The _coating in the grain of the plate has

been unaffected _by exposure and therefore it will be removed

during processing.

INK RECEPTIVE SPOTS

Figure 6. Plate after processing. As the exposure was

increased, the anchoring took place at deeper levels in the grain

thereby increasing the area of the insolubilized coating at the

peak. Since the coating is ink receptive it will print a spot of

STATEMENT OF THE PROB1EM

Since the _coating on a negative _working plate becomes

insoluble on exposure to _{light, many} areas that do not recieve

enough exposure are washed _{away during} processing. Thus, when a

continuous tone _gray scale is exposed to the plate, many of the

steps are washed away. _Whereas, a positive plate, where the

emulsion sits in the grain of the plate, holds and prints _many

more steps. The problem with a negative _working plate is that it

prints an _extremely short tonal range. _Meaning, it would _only

print three or four shades of gray. _Also, the gradation of

densities on the printed sheet from one _step to another on the

grey scale occurs in _big jumps. The _very limited range of the

plate makes it impractical for screenless printing. This

investigation deals with this _problem, and attempts to find a

feasible _way to use negative _working plates for screenless

printing.

HYPOTHESIS

It is possible to take a continuous tone black and white

positive original, and produce a set of continuous tone negatives

which represent smaller, but equal ranges of the total _density

range determined of the original, then it is possible to _fully

expose these negatives to negative _{working plates,} process the

different solid ink _density level determined _by the cutoff

density of the _{individual negatives. By printing} each _plate,

controlling ink density and register, a reproduction with the

FOOTNOTES FOR CHAPTER ONE

1. _Pobboravsky & _{Pearson, "Study} of screenless

lithography,"

IARIGAI _Conference, Rome 1967. TAGA Proceedings, (1967), 250.

2. Ibid.

3. Ibid., p. 251.

4. A. H. _Smith, "The _Theory of Screenless _Lithography in

Relation to Plate Grain Structure,"

The Journal of Photographic

Science. Vol. 26 _(1978), 162.

5. _Pobboravsky & _Pearson, p. 253.

6. L. E. _Lawson, "Screenless Photolithography,"

Professional

Printer. (March _1978), p. 4.

7. _Pobboravsky & _Pearson, p. 259.

8. R. J. _Lefebrve, "Continuous Tone Lithography,"

Printing

Impressions, Part III: Vol. _9, no. 5 (October _1966), p. 38.

9. J. A. _Mcsweeney, "Spectra-Print Screenless Lithography,"

Graphic Arts Monthly. Vol. _37, no. _{11, (1965),} p. 98.

10. Ibid.

10

CHAPTER TWO

RELATED LITERATURE

SCREENLESS LITHOGRAPHY IN RELATION TO PLATE GRAIN

Pearson and _Pobboravsky determined in their _study of

screenless _lithography that the grain of the plate was the main

factor in this process. Their hypothesis stated, "the continuous

tone effect is dependent upon the distribution of the effective

sensitivities across the surface of the plate, and that this

sensitivity distribution is in turn caused _by the variations in

coating thickness produced _by the grain of the

plate." They

concluded,"

the distribution of _coating thickness is the prime

cause of the continuous tone effect produced _by screenless

9 lithography .

"

In 1978, A. H. Smith in his _study, "The _Theory of Screenless

Lithography in Relation to Plate Grain Structure,"

studied

various grain profiles of both positive and negative _working

systems. His results showed that no single profile describes the

grain structure for the

"screenless"

11

The _majority of the literature that has been examined deals

with how screenless _{lithography works,} but there is no

information on the problem of _getting an acceptable continuous

tone print from a negative _working plate. Though in 1966, Robert

J. Lefebvre mentioned in his article about work _being done on a

negative _working continuous tone _{plate, stating} that this plate

could be exposed with a negative with a 1.0 _density range, .60 in

the shadow and 1.60 in the highlight. _{Unfortunately,} there were

no results on how well this plate performed.

TONE REPRODUCTION IN SCREENLESS LITHOGRAPHY

Zenon _Elyjiw, of the T&E _Center, performed a _study of

screenless _lithography, and one section of his report dealt with

the tone reproduction characteristics of screenless lithography.

These results were from positive _working plates, but this

information will be used for comparison with the results of this

study. The _following paragraph is taken _directly from his report.

"The characteristic curve of the printed screenless image is similar to characteristic curves of photographic

materials. It has a shoulder, a straight-line portion and

a considerable toe. _{Unfortunately,} the highlights which in most cases are the most important portions of the _picture,

must be reproduced on the toe of this curve and lose their

contrast. The dark areas of the picture which reproduce on

the shoulder of the characteristic curve also lose their contrast. This loss of highlight and shadow contrast degrades the quality of the picture and is quite

noticeable in the final print. The middle tones are

reproduced on the straight-line portion of the curve and

their contrast _actually increases in the reproduction

12

The _following Jones diagram is taken from Elyjiw,s report

These results will be used in _comparing and _evaluating the

results of this study.

13

The _bibliography section of this _study contains _many articles

that deal with practicle applications of screenless _lithography,

though in all of _these, the plates used were of the positive

14

FOOTNOTES FOR CHAPTER TWO

1. _Pobboravsky & _{Pearson, "Study} of Screenless

Lithography,"

IARIGAI _Conference, Rome 1967. TAGA Proceedings, (1967), p. 259,

2. Ibid.

3. A. H. _Smith, "The _Theory of Screenless Lithography in

Relation to Plate Grain Structure,"

The Journal of Photographic

Science, Vol. 26 _(1978), p. 169.

4. R. J. _Lefebrve, "Continuous Tone Lithography," Printing

Impressions, Part III: Vol. 9, no. 5 (October 1966), p. 38.

5. Zenon _Elyjiw, "Screenless Lithography,"

Technical report,

15

CHAPTER THREE

METHODOLOGY

The first part of _my hypothesis asks to produce film

negatives which represent smaller but equal ranges of a total

density range, in essence _separating out these areas from a black

and white original. Dr. Silver suggests _that, "if the separation

films can be produced,"

then the suggested _theory would work.

For this experiment, three plates were used, and this required

that each of the _separation

negatives represent a third of the

density range. To produce the separations it could be done in one

of two _ways, one _way would be to use a process camera and make

the separations _using continuous tone film in combination with

photographic masks. Another _possibility would be electronic

scanning. Electronic scanning would be preferred, and so this was

the first method attempted. The test was done on the Linoscan

4050, but _{unfortunately} the scanner would not produce the

extremely short _density range needed to produce the negatives.

The concept of _using the camera to produce the continuous tone

films and the masks is _easy to visualize. _But, before the films

could be made, information was needed on how the plate would

16

A 30 _{step gray} scale was printed with a negative _working

plate, and this plate held and printed four steps of this _gray

scale. This observation was made from a Dupont 30 step gray scale

that was exposed to a _{Howsen-Algraphy} negative _working plate. The

plate was mounted on the _Heidelberg "MO" offset press, which is

located in the offset press lab here at RIT. The paper used was a

60 pound coated stock. The press was run _by lab technician Dan

Gramlich. He started _printing at a low solid ink _density and

steadily increased the solid ink density. From the press sheets

that were _examined, as mentioned earlier, the plate held and

printed four steps. _{Also, running} the solid ink _density below .60

produced a _step wedge that was washed _out, due to the fact there

is not enough ink on the rollers. _Running the solid ink _density

above 1.60 caused the _step wedge to fill in. From this

information it was concluded that it would not be possible to

print dark shadow areas and achieve detail in these areas. Also,

knowing that the plate will _only print four steps, this _only

allows four steps on the film to be exposed to the _plate, and a

total of twelve between the three plates.

In this experiment, a _step wedge and a continuous tone black

and white photograph were placed on the _copy board of the camera.

A piece of low contrast continuous tone separation film was

punched and placed on registration pins on the vacuum board of

17

processed, and twelve steps from the _step wedge on the film were

identified. For _convenience, the lowest _{density step} was

considered _"step 1," and the _remaining eleven steps were counted

up from that point. From this point the goal was to produce the

largest range possible from _step 1 to _step 12. In this

experiment, a range of .60 to 1.60 was the aim point. This 1.0

density range seemed _attainable, but as noted in the _following

tables of _information, the actual _density range fell somewhat

short of this goal.

Once the exposure time and development time had been

determined, three continuous tone negatives of the original were

produced. For each individual continuous tone negative, a set of

photographic masks were produced _using high contrast line film.

The _masking set for each continuous tone negative would block out

everything except four of the twelve steps, and what was left was

a set of three continuous negatives with masks each _individually

representing one third of the twelve steps. Refer to figures 8.

9, and 10. This is a visual description of the function of the

18

F^

FIGURE 8. Mask representation for plate one

FIGURE 9. Mask representation for plate two

FIGURE 10. Mask representation for plate three.*

*Steps 19 through 30 are the twelve steps mentioned on page

17. The white areas on the scales represent masked areas, whereas

the black patch on each scale represents the section of the scale

19

The _following tables represent the exposure and

developement times of the negatives and masks, and also a table

listing the _{density readings of the twelve} steps on each

negative.

EXPOSURE AND DEVELOPEMENT TIMES TO PRODUCE THE NEGATIVES

FILM TYPE

J_

J_

1

CT Film DuPont CCLS-7 8 units 6" per/min Versamat 317

*A11 three continuous tone negatives were made at this exposure

and developement time.

TABLE 1

PHOTOGRAPHIC MASKS

FILM TYPE

1

]_

1

SH Mask DuPont COD-4 60 units 83" per/min Ultratec 324

3M L0D-4 20 units 83" per/min Ultratec 324

MT Mask DuPont COD-4 40 units 83" per/min Ultratec 324 3M LOD-4 150 units 83" per/min Ultratec 324

DuPont COD-4 60 units 83" per/min Ultratec 324 3M L0C-4 20 units 83" per/min Ultratec 324

HL Mask DuPont COD-4 20 units 83" per/min Ultratec 324 3M L0D-4 150 units 83" per/min Ultratac 324

DuPont C0D-4 40 units 83" per/min Ultratec 324 3M L0C-4 150 units 83" Per/min Ultratec 324

20

DENSITY READINGS OF NEGATIVES

STEP # 1 2 3 AVERAGE

12 (19)* _1.56

1.54 1.56 1.55

11 ₍₂₀₎ 1.46 1.45 1.47 1.46

10 ₍₂₁₎ 1.41 1.38 1.41 1.40

9 ₍₂₂₎ 1.34 1.31 1.34 1.33

8 ₍₂₃₎ 1.27 _{1.23 1.26} 1.25

7 ₍₂₄₎ 1.17 1.14 1.17 1.16

6 ₍₂₅₎ 1.07 _{1.03 1.07} 1.06

5 ₍₂₆₎ .95

.92 .95 .94

4 ₍₂₇₎ .84 .81 .84 .83

3 ₍₂₈₎ .77 .74 .76 .76

2 ₍₂₉₎ .69 .67 -69 .68

1 ₍₃₀₎ .66 .63 .66 .65

1

1

*These numbers are the actual numbers on the _step wedge of the

negatives.

TABLE 2

When _exposing the negatives to the plates, it was not

possible to use the 90 unit exposure that was used to expose the

gray scale in the original test. The reason is that more exposure

was needed to compensate for the masks, and also a diffusion

sheet. An attempt was made to pre-determine the correct exposure

for the plates _using an UGRA plate exposure wedge in combination

with sheets of Mylar to simulate the masks. _Yet, these Mylar

sheets did not simulate the high _density of the masks _very well,

and so the exposure determined to be correct was not in fact

suitable for the set of negatives. The plates were exposed until

the image on the plate appeared to be useful. The _following

21

PLATE EXPOSURES/FIRST PRESS RUN

Plate 1 Plate 2 Plate 3

880 ₄₄₀ 220

TABLE 3

The plates were mounted on the _Heidelberg "MO" press, each

image run one at a time but in perfect registration with one

another. The highlight plate was run at a solid ink _density of

1.0, the midtone plate at _1.30, and the shadow plate at 1.60.

EVALUATION OF THE RESULTS

In the evaluation process, the main objective was to

determine if a continuous gradation of tones in the printed _step

wedge existed. If in fact it existed, then it was the goal of the

author to compare the tone reproduction of the print to that of a

22

FOOTNOTES FOR CHAPTER THREE

23

CHAPTER FOUR

PRESS TEST AND EXPERIMENTAL RESULT

With the pre-press work _completed, the plates were mounted

on press for the experimental run. The press used was T&E

Center's two color _Heidelberg "MO" offset press, which was

equipped with an ALCOLOR _dampening system. The fountain solution

contained fifteen percent alcohol, and had a PH of 4.5. The ink

used was MARATHON premium hard _{dry black,} and it had a tack

rating of ten. The thickness of the plate was twelve thousands,

and the plate was packed two to four thousands over bearers. The

blanket was packed one to two thousands over bearers. The paper

used was a _sixty pound coated stock.

The first plate was mouted on the second _{printing unit,} and

in the first run the aimpoint of the solid ink _density was .90.

Although the press had two _printing units, it was decided to use

only one unit. Aproximately five-hundred sheets were printed once

the .90 solid ink density was reached, and during the run a sheet

was pulled about _every twenty-five sheets to measure the solid

ink density. These sheets were run through the press two more

24

followed as in the first run. The solid ink _density for the

second run was _1.20, and for the third run it was 1.60. The press

sheets that follow represent the _{first, second,} and third passes

through the press. Refer to figures _{11, 12,} and 13.

EVALUATION OF PRESS RUN

It is obvious from _looking at the printed sheets, that the

results were not favorable. For _example, notice the printed _step

wedge from the second pass through the press (Figure ₁₂₎ . The

fourth _step of that section is _{virtually lost,} and this would

indicate that the _printing plate used in the second pass through

the press was underexposed. _Also, notice on plate three (Figure

13), the final section of the _step wedge. On the final pass

through the press the solid _density was run at _1.60, and it can

be observed that this caused the area in question to fill in and

lose detail. What also had an effect on this third section of the

step wedge was the fact that the subject in question was printed

on coated paper. The high holdout of the paper in conjunction

with the high solid ink _density most _likely caused the ink to

spread and fill in. Table 4 lists the _density readings of the

25

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28

DENSITY READINGS FROM PRINTED STEP WEDGE

1_ 2 3 4 5 AVE.

1.40 1.50 1.47 1.50 1.49 1.47

1 .40 1.50 1.47

1.50 1.49 1.47

1.38 1.50 1.47 1.50 1.47 1.46

1.24 1.32 1.36 1.34 1.35 1.32

1.12 _{1.19 1.21 1.19 1.21 1.18}

1.12 1.18 1.20 1.19 1.19 1.18

1.00 1.07 1.08 1.08 1.09 1.06

.57 .60 .62 .59 .61 .60

.89 .88 .83 .86 .87 .87

.87 .86 .81 .85 .86 .85

.84 .83 .78 .82 .84 .82

.73 .74 .70 .72 .73 .72

TABLE 4

From these numbers it is obvious that a continuous gradation

of tones was not _produced, and thus it would not make sense to

compare this tone reproduction to that of a positive _working

system. It was _{decided, though,} to attempt another press run to

try to correct the problems that occured in the first test. The

first correction was to lower the solid ink _{density overall,} and

secondly to use uncoated paper. This was in the hopes to reduce

the problem of the ink _spreading and _filling in. Also, the

exposure used on the second plate will be increased so to

hopefully hold and print the fourth step. The image printed was

changed to a portrait of a person in the hopes that this might be

a better indicator of how effective this process is.

New negatives were produced _using the same procedure as

29

Dr

Dr Do

.72 1.00 .82 1.07 .85 1.14

.10 .20 .30 .40 .50 .60 .70 .80 .90 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4

Do

30

were lowered this time to emphasize the highlight area of the

original more. This is due to the fact that it appears dark

shadows cannot be printed with this _process, because of the loss

of detail at high solid ink densities. The _following tables list

exposure and development _times, and also the densities readings

from the negatives.

EXPOSURE AND DEVELOPEMENT TIMES FOR NEGATIVES FOR PRESS RUN TWO

FILM TYPE

]_

J_

1

DuPont CCLS-7 14 units 12"/min Versamat 317

*A11 three continuous tone negatives were made at this exposure

and development time.

TABLE 5

PHOTOGRAPHIC MASKS

FILM TYPE

1

1

1

SH Mask DuPont COD-4 40.0 units 83"/min Ultratec 324

Plate 3

3M L0D-4 19.5 units 83"/min Ultratec 324

MT Mask DuPont COD-4 15.0 units 83"/min Ultratec 324

3M Lod-4 26.5 units 83"/min Ultratec 324

Plate 2

DuPont COD-4 40.0 units 83"/min Ultratec 324

3M L0C-4 13.0 units 83"/min Ultratec 324

HL Mask DuPont COD-4 10.0 units 83"/min Ultratec 324

3M L0D-4 19.5 units 83"/min Ultratec 324

Plate 1

DuPOnt C0D-4 20.0 units 83"/min Ultratec

3M L0C-4 19.5 units 83"/min Ultratec

31

DENSITY READINGS FROM NEGATIVES

STEP # FILM 1 FILM 2 FILM 3 AVE

1 (30)*

.39 .38 .35 .37

2 ₍₂₉₎ .42 .41 .37 .40

3 ₍₂₈₎ .49 .47 .44 .47

4 (27) .55 .53 .52 .53

5 ₍₂₆₎ .65 .62 .61 .63

6 ₍₂₅₎ .76 .72 .72 .73

7 ₍₂₄₎ .86 .82 .82 .83

8 ₍₂₃₎ .95 .90 .90 .92

9 (22) 1 .03 .98 .99 1.00

10 ₍₂₁₎ 1 .10 1.06 1.06 1.07

11 ₍₂₀₎ 1 .17 1.12 1.12 1.14

12 ₍₁₉₎ 1 .24 1.23 1.22 1.23

*These are the actual numbers on the _step wedge of the negatives.

TABLE 6

These negatives were stripped as _before, and were used to

expose the same _{Howsen-Algraphy} plates used in the first press

run. It seemed logical that exposures would be _relatively the

same as the exposures for the first set of negatives, considering

that the same structure of continuous tone negative and masks

existed. _Yet, these same exposures did not come close in

producing a suitable image on the plate as _they did on the

original set of plates. At this point it was decided to _try a

different brand of _printing plates, and this was the Kodak SX

negative _working offset plate. These plates were exposed on a

NuArc plate _exposing unit which had a 4000 watt metal halide

exposure lamp. These plates seemed to respond well with the

negatives from _examining the image on the plate, and so these

plates were used for the second press run. The _following table

32

PLATE EXPOSURE TIMES/2ND PRESS RUN

HL PLATE

]_

1600 units 800 units 220 units

TABLE 7

2ND PRESS RUN AND TEST EVALUATION

The Kodak SX plates were taken to the _press, and the

highlight plate was mounted and run first. The first plate was

run at a solid ink _density of .70, the next plate at 1.00, and

the last plate at 1.30. In _observing the first run through the

press, getting the .70 solid ink density was difficult. Yet, once

it was achieved the press held this _{density very} consistently. A

fifty pound uncoated stock was used for this run. The ink used

was Marathon premium hard _{dry black,} and it had a tack _rating of

ten.

The first pass through the press on this run was somewhat

encouraging, note Figure 16. There was some gradation in _tones,

and the image showed some detail. The second plate was then

mounted, but after _running a few sheets, two of the four steps on

the plate would not print. So a new plate had to be made, and it

seemed that the same exposure used for the first plate would be

applicable for the set of films used to expose the second plate.

This _being, because the _masking setup was the same on all films

33

with this negative it produced one solid _step instead of four

separate ones. The next exposure used was 1000 units, and this

produced what appeared to be four separate steps on the plate.

The plate was then post exposed for 800 units, this was done to

harden the image on the plate. The third plate was also post

exposed for the same reason. _Relating to the third _plate, the

masking setup on this negative blocked out all the image of the

continuous tone film except the four steps of the _step wedge.

There was some unwanted _density in the clear area of the mask,

and so it was replaced with a rubylith mask.

The plates were then brought back to _press, and run in the

same manner _previously stated. The second plate was run at a

solid ink _density of 1.0. and the third plate was run between

1.30 and 1.40. From _observing the press _sheets, it is clear that

the second plate was overexposed, and as a result a solid patch

is printed instead of four separate ones. The third plate

produced an image that appears to show that the plate was

underexposed. The _following table is a list of _density readings

taken from a sample of five sheets. Note the _density difference

34

DENSITY READINGS FROM SECOND PRESS RUN

PLATE # _{1_} 2 3 4 _5. AVE

1.17 1.12 1.10 1.15 1.13 1.13

Three 1.07 1.01 .98 .98 1.02 1.01

.66 .66 .61 .65 .61 .64

.24 .22 .22 .22 .22 .22

.94 .93 .88 .90 .91 .91

Two .92 .92 .86 .88 .89 .89

.89 .91 .85 .88 .87 .88

.90 .88 .83 .87 .91 .88

.61 .61 .59 .57 .59 .59

One .57 .57 .56 .53 .54 .55

.38 .39 .35 .40 .38 .38

.44 .43 .42 .39 .36 .41

TABLE 8

It is clear from _observing Figures _16, 17, and _18, that

there were no improvements in the second press run as compared to

the first press run. If it has not been made clear _yet, it seems

appropriate to point _out, that _finding a correct plate exposure

was a major problem. It was decided to _try and find out if the

plates used were _consistent, or as it seems in this case

inconsistent. Four KODAK SX plates were taken from the batch used

in the second press _run, and a section of each plate was placed

on the NuArc platemaker. On each plate section was placed a

DuPont 30 _Step continuous tone _step wedge, and the plates were

given a 75 unit exposure. The plate sections were removed from

35 Dr 1.6. 1.5. 1.4. 1.3. 1.2. 1.1. 1.0. .90. .80. .70. .60. 50. .40. .30. .20. .10. Dr Do .41 1.00 .38 1.07 .55 1.14 .59 1.21 .88 1.30 .88 1.42 .89 1.54 .91 1.69 21 1.86 .64 2.01 1.01 2.18 1.13 2.28

.10 .20 .30 .40 .50 .60 .70 .80 .90 1.0 1.1 \2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 22 2.3 2.4

Do

36

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38

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39

Then all the plates were run through the KODAK Polymatic plate

processor at the same time. Though it is not possible to examine

the result of this test from the duplication of the _plates, there

was a difference in how the plates performed. There was a

noticeable _{difference between plates three}

and four. The scale on

plate three had an image _up to _{step thirteen, whereas the scale}

on plate four _only had an image _up to _step eleven. This would

seem to back _up the _{reason that the}

exposures on the plates were

not _consistent, and thus made it almost impossible to get a

handle on the correct exposure times from plate to plate. The

following table displays the densities of the continuous tone

step wedges used in the experiment. This is to show that the

scales used were _consistent, and the numbers show that _they are.

DENSITIES OF DUPONT SCALES USED IN PLATE TEST

STEP # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 .03 .13 .23 .33 .42 .53 .63 .74 .85 .95 2 .03 .14 .25 .35 .45 .55 .65 .75 .85 .95 3 4 .03 .03 .13 .13 .23 .23 .33 .33 .42 .42 53 .64 74 .85 95 .53 .63 .74 .85 .95

1.04 1.04 1.04 1.04

1.15 1.15 1.14 1.13

1.25 1.26 1.24 1.23

1.35 1.35 1.33 1.32

1.49 1.46 1.44 1.44

STEP #12 3 4

16 1.61 1.56 1.55 1.55

17 1.70 1.64 1.64 1.64

18 1.78 1.72 1.73 1.73 19 1.88 1.82 1.83 1.83

20 1.99 1.94 1.94 1.95

21 2.10 2.06 2.05 2.06

22 2.20 2.16 2.13 2.15

23 2.30 2.28 2.24 2.26

24 2.42 2.42 2.36 2.38

25 2.53 2.53 2.47 2.50

26 2.61 2.63 2.57 2.59

27 2.71 2.73 2.68 2.68

28 2.81 2.82 2.77 2.78 29 2.90 2.90 2.87 2.86

30 2.98 2.99 2.96 2.95

40

IB I9 I 10 111III 113 114115 M 117 ll ll 120 131 1 123 124 l 136 117 128lU0l DU PONT PHOTO PRODUCTS TRANSMISSION GRAY SCALE A-M013

FIGURE 19. Plate One. Plate exposure test

I I I2 I 3 I4IS I617 IS I 9 1 10 1 11 1 13 1 13 1 14 1 151161 17 1181 19130 Ijl 132 123 134 135 136 137 I 38 139130I DU PONT PHOTOPRODUCTSTRANSMISSIONGRAYSCALE A-6401 3

FIGURE 20. Plate Two. Plate exposure test,

I I 13 13 I4 15 I*I 7 IB 19 I 10 1 1 1 1121 13 1 14115 '16 1171 18 119130 131 133 123124 1 25126 1371 38 1291 30 I DU PONT PHOTO PRODUCTS TRANSMISSION GRAY SCALE A-6401 3

FIGURE 21. Plate 3. Plate exposure test.

,'"l2 I 3 I I5 I6 I 7 I 6 l"91 10 111H2 Il3 H4 Il5 116 117he119120 12. 133 133 1341 35136137 I28129 130I

1,23,45

DU PONT PHOTO PRODUCTSTRANSMISSIONGRAY SCALE A-64013

41

CHAPTER FIVE

CONCLUSIONS AND RECOMENDATIONS

From _examining the press sheets it is obvious that this

experiment failed to confirm the original hypothesis. It is true

that the films can be produced, but not without great difficulty.

What was proven in this _experiment, is that it is not possible to

print a continuous gradation of tones with three negative _working

plates, and _{highly unlikely} with more than three. It was

suggested that if each plate could print a _density range of about

.60, then it would be concievable to produce a continuous

gradation of tones. With the negative _working plates used in this

experiment, it was not possible to get even close to a _density

range of .60 from a single plate.

It had been pointed out earlier in this report that each

plate will print four steps of a continuous tone _step wedge, but

from the results of this experiment it appears that at the most

the plates will print and hold _only three steps. Even had it been

possible to print the twelve steps from the three plates in a

continuous gradation, it would not have produced a suitable

image. Under the best circumstances, it would take _many more

42

In conclusion, the author would have been satisfied if a

gradation of tones were produced in the printed _step wedge, and

from the results of this experiment it seems an unattainable

goal. The negative _working plate is made for halftone printing,

and these brands used in this experiment _were, obviously, not

43

BIBLIOGRAPHY

Banks, W. H. "A _Theory of _Screenless Photolithography," _PIRA

Abstracts. _1980, 104-15.

Elyjiw, Zenon. "Screenless Lithography,"

Unpublished technical

report at the T&E _Center, Rochester Institute of Techology.

Lawson, L. E. "High Rendition Photo-Lithographic Images,"

Professional Printer, Vol. 26, 1981, 2-8.

Lawson, L. E. "Screenless Photolithography,"

Professional

Printer, Vol. 22, 1978, 2-9.

Lefebvre, Robert J. "Continuous Tone Lithography,"

Part III

Printing Impressions, Vol. _9, October _1966,

38-39-McSweeney, Joseph A. _{"Spectra-Print,} Screenless Lithography,"

The Graphic Arts Monthly, November _1965, 96-98.

Montgomery, Alex. "Intergral Random Dot,"

Australasian Printer,

August _1978, 13-15.

Nash, Clive F. "Practical Experience of Screeenless Offset

Photolithography,"

Professional _Printer, Vol. _24, 1979, 6-13.

Pobboravsky, Irving and _Pearson, Milton. "Study of Screenless

Lithography,"

IARIGAI at _Rome, TAGA Abstracts, 1967, 249-62.

Silver, Julius. Interview, Rochester Institute of Technology. 24

January, 1986.

Smith, A. H. "The _Theory of Screenless Lithography in Relation

to Plate Grain Structure," The Journal of Photographic

Science, Vol. _26, 1978, 162-171.

Vickers, E. Wayne. "Screenless _Printing Procedures at the U.S.

Geological Survey," The Journal of Photographic Science, Vol.